Tornadoes 'rare' risk for Sth Canty

DEVASTATING: A tornado near Waimate in 2006 ripped through the 140-year-old Downlands homestead.

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South Canterbury has just as much chance of being hit by a tornado as anywhere else in New Zealand, a NIWA meteorologist says.

Dr Richard Turner says tornadoes, like the one that hit Auckland's western suburbs yesterday, are relatively rare events in New Zealand.

On average there are around seven moderate to strong tornado events reported in New Zealand each year. They are less frequent on the eastern side of the country but can occur anywhere, he says.

South Canterbury last experienced one on March 8, 2006. It damaged a homestead and sent a pig flying through the air near Waimate.

The tornado struck about 2pm and ripped the roof and much of the second storey away from the 140-year-old Downlands Homestead, which was rented by Dennis and Denise Fahey and their two children.

Residents reported that a kune kune pig in a yard was also picked up by the tornado and flung through the air landing unharmed in a nearby paddock.

Dr Turner says most tornadoes made ground on the western side of New Zealand during thunder storms and generally in the afternoon. They can hit anywhere at anytime, however, he says.

''A lot of them tend to peak in winter time; there seemed to be a lot of them in the 1950s and 1960s. It calmed down in the 1970s, 1980s and 1990s.

''Since 2000 it has become more active again.''

Mr Turner said tornadoes in New Zealand are usually around a few tens of metres wide and have tracks of just a couple of kilometres. They are extremely localised and the damage is very confined to the actual tornado itself. A tornado will typically last for a few minutes, track across the land for two to five kilometres and will have a diameter of 20 to 100 metres. Wind speeds are in the order of 115 to 180kmh.

At the more extreme end, some tornadoes track for over 100 kilometres, are over one kilometre wide and have winds up to 480kmh - such tornadoes are extremely rare anywhere in the world.

NIWA maintains a catalogue of major weather events in New Zealand over the last 200 years called the New Zealand Historic Weather Events Catalogue.

The information has been collated from newspaper reports, journals, books and databases kindly provided by various organisations and individuals.

For each event NIWA identifies the regions affected, the hazard types associated with the event and the resulting impacts.

The most damaging and lethal tornado in New Zealand occurred at Frankton (Hamilton) on August 25, 1948.

The tornado carved a 100-200 metre swath through the suburb, causing three deaths, 12 injuries, damaging 150 houses and 50 businesses with an overall damage cost of $60 million.